A process of this kind is disclosed in German No. DE-A1-3 433 368, in which the air flow fed to the internal combustion engine is determined, the determined value being fed to a control device for influencing the operating parameters of the internal combustion engine. It is known to use a so-called hot-wire or hot-film air flow rate meter for this. In the case of the hot-wire air flow rate meter, the intake air flow is directed past a heated wire (hot wire). This wire is part of an electrical bridge circuit. It constitutes the temperature-dependent resistor already mentioned, through which a heating current flows. The hot wire is held at a constant higher temperature than the intake air temperature by the heating current. The required heating current is a measure of the air flow sucked in by the engine. It is converted into a voltage signal which is processed by the control unit as an important input variable in addition to the engine speed. A temperature sensor, i.e., the temperature sensor already mentioned, installed in the hot-wire air flow meter ensures that the output signal is not dependent on the intake air temperature. In addition, it serves to keep the resistor through which the heating current flows at the constant higher temperature. A hot-film air flow rate meter is of a corresponding design. Instead of the hot wire, a film-like resistor is used.
U.S. Pat. No. 4,658,641 discloses a process for determining the flow rate of a fluid which is used to determine the air flow rate in an internal combustion engine. In order to prevent the temperature-dependent resistor heating up too strongly when the air flow is switched off (when the internal conmbustion engine is stationary), the heating current is switched off as soon as the air flow rate undershoots a predetermined threshold value.
European No. EP-A300 144 027 discloses a device for measuring the sucked-in air flow in an internal combustion engine which has a bridge circuit. The bridge circuit comprises a heatable resistor in the intake path of the internal combustion engine, a resistor for measuring the temperature of the sucked-in air and further bridge resistors. A heating current is fed to the bridge circuit via a transistor which is periodically driven by a signal which is generated by a microcomputer. A signal which represents the temperature change of the resistor which can be heated up by a heating current is detected by the microcomputer. A first correction signal is determined from the difference between a value detected by the microcomputer and a signal which takes into account the temperature of the heatable resistor at normal temperature and in the case of equilibrium of the bridges. A correction value which influences the duration of the control signal is determined as a function of the first correction signal with the aid of a table. This second correction signal is used for the correction of the duration of the passage of current.
German No. DE-A1-4 004 552 also discloses a signal processing method for a flow rate sensor of the thermal type which has a resistor with temperature dependency. When the fluid flow is in the steady state, that is, in the so-called state of equilibrium, the following steps in this signal processing method are carried out: setting in advance the relation of a value assigned to the flow rate, which value changes in accordance with the change in the flow rate, and in accordance with a first operating value which indicates the temperature characteristic of the carrier component bearing the temperature-dependent resistor, which value or which characteristic changes as a function in order to produce a value, as parameter, assigned to the flow rate; calculation of the first operating parameter from a value assigned to the flow rate when the flow rate is detected in accordance with the predetermined relation; comparison of the calculated first operating value with the second operating value which is set in relation to the first operating value; correction of the second operating value so that it can be approximated to the first operating calculation of a compensation factor by means of a predetermined calculation formula with the calculated first operating value and the correct second operating value; and compensation of the compensation factor by means of multiplication.